The invention relates to a process for impregnating threads in the form of spools with a liquid composition such as a crosslinkable resin. The invention is particularly suitable for pre-impregnating reinforcing threads for use in crosslinkable plastics.
It is well known to reinforce plastics using textiles of various forms to give end products which are sometimes known as "laminates". In general, the impregnation of the textile material is carried out just before product manufacturing step, that is to say either in the mould itself, where the product is moulded to shape, or on a mandrel where tubes, containers or other hollow articles are being made. Although very widespread, these techniques do exhibit disadvantages. Firstly, since rotating or rubbing members are often used, there is often a large proportion of bubbles in the laminate which leads to imperfections in the finished product. Moreover, since the impregnation time is relatively short, the fibre to plastic bond is sometimes defective, and the impregnation capacity is fairly limited so that thorough and homogeneous impregnation is difficult to carry out. Finally, the composition of the resulting laminate tends not to be homogeneous, within or between laminates, which quite obviously limits their applications.
It has also been proposed to impregnate the threads by passage through a tank of suitable resin, but in this technique, it is necessary to pass the threads over numerous guides, and this causes the fretting and sometimes even breaking of the individual strands.
it has also been suggested to wind the threads onto a mandrel and then to spray the resin thereon, but in this case, the resulting laminate again possesses numerous bubbles, which detracts from its properties and spoils its appearance.
Finally, in all these techniques in which the impregnation is carried out from the outside towards the inside, the installations are generally bulky, expensive and rather impractical.
It has also been proposed to carry out the treatment from the inside towards the outside (see, for example, Swiss Pat. Nos. 374,046 and 561/74) by placing the textile as a reel on a perforated mandrel. Unfortunately, this technique as developed thus far, which is satisfactory for dyeing or moistening reels, is not suitable for resin impregnation because the resin disposition is not sufficiently uniform and the installation frequently becomes clogged.
The present invention aims to overcome these disadvantages.